Harper Lake Solar Electric Generating Station, California

For more than twenty years, this was the largest commercial solar power plant in the USA (in output), generating around 160 megawatts at its peak. It is one of three separately owned sites within 40 miles of one another, that make up the nine solar fields in the Solar Electric Generating System (SEGS). Harper Lake was the last of these built, and is designated as SEGS 8 and 9. Together the three SEGS sites (this one, SEGS 1 and 2 at Daggett, and SEGS 3-7 at Kramer Junction) can generate about 354 megawatts at peak output. Built in response to the energy crisis of the late 1970s, and finally going online in the 1980s, SEGS comprised all of the industrial-scale solar power produced in the USA for nearly 20 years. Starting around 2010, more large-scale solar power generating stations have been built, and there are now dozens in the southwestern USA producing more than 100 megawatts each. SEGS are solar thermal plants, using reflective parabolic troughs to generate heat, then steam, then power. These solar facilities are referred to as "advantageous peak facilities" as they operate at their peak when it is sunniest, which is also when local power requirements are greatest, due to increased air conditioning demand. This plant was built on top of the remains of a large ranch house and an aircraft R&D area at Harper Lake, which included facilities owned by Howard Hughes. The Harper Lake plant has a new neighbor as of 2014, the Spanish-owned energy company Abengoa's Mojave CSP solar power plant, which boasts an output capacity of around 250 megawatts.